Foam layers sag & give-out in less than 2 years

I bought a Beautyrest "Black Desiree Firm" mattress with a suggested retail of over $2k. So I thought I was buying quality that would last, It didn't! I am not a large person. I am height / weight proportionate weighing 165 lbs. So I was very surprised to realize my mattress was sagging in less than 2 years use. And has gotten progressively worse in the past 3 months of run arounds from Simmons' / Beautyrest Warranty department. When I bought this mattress, the online description boasted a 20 yr. non prorated warranty. From day 1 of contacting the warranty department to exercise a claim, I have experienced a non-accomating process. Nothing short of"stall" tactics. It has now dragged on for 3 months & still no resolve in hand. To add insult to this process, they 1st told me my mattress only has a 10 year warranty & they go on to explain that a new replacement mattress will only carry the balance of the 10 yr. warranty. After an Independant Inspector came out they admitted that I do have a justified claim, but informed me that my mattress has been discontinued and I would have to identify a suitable replacement. In addition, they have the nerve to tell me that they will only honor a replacement upto the $1,000 I paid. Any additional would be billed to me! I pointed out that I bought my mattress on a Special online Promo Sale (as we all know the retails are fictitious). I also noted that their suggested retails had increased by 30-50% in the 2.5 yrs since buying mine. That said, all I wanted was Like-Kind & quality of construction as to what I had purchased. They then sent me on a wild goose chase to go identify a replacement product of my liking. (Along with a list of a half dozen of the biggest mattress sellers, NOT to go to). I spent 3 days researching & reading reviews online to identify Like-Kind construction and Firmness levels. And then another 2 days out in the field to find these prospective replacements. Reported back my 1st & 2nd choice and her on the 90th day, still no answer!